This invention relates to a grooved magnetic substrate for thin film magnetic heads such as, for instance, vertical magnetic heads, MR element magnetic heads or inductance magnetic heads and a method for producing such a substrate. More particularly, this invention relates to a magnetic substrate of a grooved structure wherein a groove formed in a substrate is filled with a nonmagnetic layer.
Recently, thin film magnetic heads are being put to practical use, and are known to have electro-magnetic conversion properties higher than, by one digit or more, those of conventional magnetic heads prepared by using soft ferrite blocks as the starting materials. In order to improve the properties of such thin film magnetic heads, it has been also proposed to provide a stepped structure in the cross-sectional shape thereof.
However, since thin film heads of stepped structure show a low strength with respect to the sliding movement of magnetic recording media, it has been proposed to provide thin film magnetic heads using magnetic substrates having therein a groove filled with a non-magnetic layer, whereby the distance between the opposite poles is magnetically increased, and the substrate is physically or geometrically of a planar surface. In general, glass has been used as the non-magnetic layer.
In order to embed glass into the surface of a magnetic substrate such as Mn-Zn ferrite, Ni-Zn ferrite or the like in the groove form, there is a process wherein plate-like glass is placed in at least one groove formed in a surface of such a magnetic substrate, and is heated to a temperature at which a glass viscosity reaches 10.sup.4 -10.sup.5 poise, thereby to form a non-magnetic layer to fill the groove. However, such a process offers problems in that pores easily appear in the formed glass layer, and, when Mn-Zn ferrite is used as the magnetic substrate, an interdiffusion layer of the substrate components and glass components is formed in a region where they come into contact with each other.
In the preparation of thin film magnetic heads, a glass layer is formed on a substrate, and thereafter, several kinds of thin films constituting a magnetic circuit are formed on the precision-finished glass layer by means of IC technology. However, if pores are produced in that layer, the exposed pores will lead to disconnection or poor insulation of the magnetic circuit and a variation in magnetic properties. In addition, the yield of head products will also be dependent largely upon the number of pores, thus offering a grave problem in view of quality control.
An apex point defining the boundary between the substrate of the groove portion and the glass layer in the magnetic circuit of the thin film head provides a reference point, when determining the gap depth of the thin film head. The input and output powers of the head are largely affected by this gap depth. However, there is a variation in the location of the apex point according to the thickness of the interdiffusion layer formed on the contact surface between the groove portion of the substrate and the glass layer. Such a variation leads to a problem that it fluctuates the gap depth with the resulting variation in the resultant electromagnetic properties.
With a view of providing a magnetic substrate for a grooved structure wherein the number of pores of glass charged in a groove in the substrate is prominently decreased, and the amount of an interdiffusion layer between the magnetic substrate and the glass is reduced, the present applicant has already proposed to prepare a grooved magnetic substrate by filling, under a given load, at least one groove formed in a surface of a magnetic substrate with glass heated to a temperature at which said glass has a glass viscosity of 10.sup.6 poise to 10.sup.8 pose and, thereafter, subjecting said magnetic substrate to hot isostatic pressing at or below a temperature at which the glass viscosity of said glass is 10.sup.6 poise (Japanese Patent Kokai Publication No. 59-203213 which corresponds to U.S. Pat. No. 4,636,420).